Thermal barrier coatings which are applied to components are known from the field of gas turbines, as described for example in EP 1 029 115.
Thermal barrier coatings enable components to be used at higher temperatures than those permitted by the base material, or allow the service life to be extended.
Known base materials (substrates) for gas turbines allow temperatures of use of at most 1000° C. to 1100° C., whereas a coating with a thermal barrier coating allows temperatures of use of up to 1350° C.
The temperatures of use of components in a steam turbine are much lower, and consequently these demands are not imposed in this application.
It is known from EP 1 029 104 A to apply a ceramic erosion-resistant layer to a ceramic thermal barrier coating of a gas turbine blade or vane.
It is known from DE 195 35 227 A1 to provide a thermal barrier coating in a steam turbine in order to allow the use of materials which have worse mechanical properties but are less expensive for the substrate to which the thermal barrier coating is applied.
U.S. Pat. No. 5,350,599 discloses an erosion-resistant ceramic thermal barrier coating.
US 2003/0152814 A1 discloses a thermal barrier coating system comprising a substrate made from a super alloy, an aluminum oxide layer on the substrate and a ceramic as outer ceramic thermal barrier coating.
EP 0 783 043 A1 discloses an erosion-resistant layer consisting of aluminum oxide or silicon carbide on a ceramic thermal barrier coating.
U.S. Pat. No. 5,740,515 discloses an erosion-resistant layer of a silicide, in particular molybdenum silicide, which has been applied to a ceramic thermal barrier coating.
US 2003/0035892 A1 discloses a ceramic thermal barrier coating system.
U.S. Pat. No. 5,683,226 discloses a component of a steam turbine with an improved resistance to erosion.
The thermal barrier coating is strongly eroded on account of impurities in a medium and/or high flow velocities of the flowing medium which flows past components having a thermal barrier coating.